Gerbilling is an urban legend. This means it a story that is not true. It is the act of placing a gerbil into the human rectum for sexual pleasure. Other small live animals (usually gerbils but also mice, hamsters, rats and various other rodents) are used.
Folklorist Jan Harold Brunvand writes that the urban legend began in 1984. It involved a mouse and an unidentified gay man. In passing years this story changes into a gerbil, and was made to involve to many named male celebrities that were publicly thought to be gay. Rumors about various male celebrities engaging in gerbilling have become popular urban legends over the years.